Integrators may need minimum deposit amount to introduce validation if
the amount user wants to deposit meets Bridge requirement of a deposit
to exceed the dust threshold.

The amount may be useful for integrators for validations of the deposit
amount. See example use case in thesis/acre#253 (comment)

It turns out that this version where we read from the storage costs
`117 366` gas. Which is less than an alternative approach:
```
        initialDepositAmount =
            fundingTx
                .outputVector
                .extractOutputAtIndex(reveal.fundingOutputIndex)
                .extractValue() *
            SATOSHI_MULTIPLIER;
```
which costs `117 601` gas.

_initializeDeposit now returns additional property:
initialDepositAmount.
We need to update the usage example.